1. Field of the Invention
The present invention relates to novel phthalaldehyde tetraalkyl acetals, to a process for preparing them by electrochemical oxidation, and to the use thereof as compounds for storing the corresponding aldehydes.
Acetals are not just of particular interest in protective group chemistry because they protect reactive aldehydes from unwanted reactions; they are also used as compounds which are stable to heat and oxidation for storing aldehydes which can be liberated quantitatively from the acetals as required under mild conditions.
Of particular interest are phthalaldehydes which are used, for example, as disclosed in DE 3 421 976 A1 as intermediates for the preparation of dyes, optical brighteners or specific polymers.
2. Description of the Prior Art
Phthalaldehyde tetraalkyl acetals can be prepared, for example as disclosed in DE 3 108 790 A1, by reacting .alpha., .alpha., .alpha.', .alpha.'-tetrahaloxylenes with alkali metal alcoholates. However, this process has the disadvantage that the tetrahaloxylenes are toxicologically unacceptable and can be obtained with only unsatisfactory selectivity.
According to DE 3 421 976 A1, phthalaldehyde tetraalkyl acetals can be prepared electrochemically by oxidation of the corresponding bis(alkoxymethyl)benzenes. However, since these starting materials are synthesized from bis(halomethyl)benzenes, the abovementioned problems arise in this case, too.